There are two main types of internal combustion engines currently in use; the compression ignition engine and the spark ignition engine. In the latter, an explosive mixture of fuel and oxygen located in a confined space ignites through exposure to an electric spark. The resulting explosion provides force that the engine converts into useful work.
To properly control this process, the timing and duration of the spark must be controlled. These needs become particularly acute in a multichambered engine where numerous explosions in various combustion chambers must be sequentially ordered to assure proper functioning of the mechanical aspects of the engine. A distributor has traditionally been used to aid in this control process. A distributor, however, makes use of moving parts that are subject to wear. Further, the quality of the spark provided through use of such a system can deteriorate over time due to physical wear and tear of the distributor and its related components.
In response to these problems, distributorless ignition systems have begun to be used to control the spark. In such a system (see FIG. 1), an engine position sensing unit (A), such as a toothed wheel sensor and related components, sense engine position and engine speed and provide a PIP (profile ignition pickup) signal that relates to crankshaft location and a CID (cylinder identification) signal that relates to identification of a particular cylinder, such as the number one cylinder. These two signals may then be provided to an electronic engine control (B) that creates a SPOUT (spark output) signal that contains spark advance/retard and dwell information. An output logic unit (C) may then control a distributorless ignition system (D) in response to the SPOUT and CID signals to produce a proper spark.
Although such distributorless ignition systems as described above avoid the problems noted with respect to distributor based ignition systems, these distributorless ignition systems have given rise to new problems. For instance, the CID signal can be temporarily lost, as can the SPOUT signal. In addition, the SPOUT signal can fault either high or low, yielding different system response problems. When such faults occur, the engine will often be rendered nonsuitable for its intended purposes.
There therefore exists a need for a system that will allow a distributorless ignition system to compensate, at least to some satisfactory degree, for transitory loss of input signals.